17 



prolonged down ward as tlie deltoid crest. The outer tuberosity in 

 the horse is doable, and while not hooked as in the rhinoceros, is a little 

 more prominent than in the present species: the inner is not hooked 

 as in tlie P. sejunctus. There is an ala on the inner side of the distal end 

 of the hnmerus, and a supracondylar foramen, both of which are want- 

 ing' in the horse. 



The radius differs from that of the horse, in being considerably longer 

 than the humerus, instead of a little shorter. It is gently curved and 

 flattened, with the transverse ends about equally wide. The ulna is 

 coosified with it throughout the length, excepting a small portion be 

 yond the humeral cotylus, as in the horse. 



Tlie femur is stout, with the lesser trochanteric ridge well developed. 

 The trochlea is wide, with subequally elevated bounding ridges. The tibia 

 is considerably longer than the femur, and presents a long and promi- 

 nent cuemial crest. The shaft is transverse, with external edge and inner 

 plane narrower than the anterior. The trochlear is very oblique; the 

 astragalar grooves well defined by the internal and external tuberosi- 

 ties. Fibula not jn-eserved. 



The right posterior foot, among otliers is perfectly preserved. It is 

 like the radius and fore foot, and the tibia, distinguished for its elonga- 

 tion and slender proportions, as compared with tiie horse. The astrag- 

 alus differs from that of the horse in having the cuboid facet on a more 

 pronounced neck, and in the narrowness of the trochlea. The navicular 

 'facet is subpentagonal and without emarginatiou. The cuboid is largely 

 extended posteriorly where it bears a large tuberosity. The naviculare 

 is shallow and concave proximally. The ectocuneiforme is of similar 

 length ; behind it a well developed mesocmiciforme which supports the 

 internal metatarsal. The external metatarsals are situated behind the 

 median except for an inch at their distal extremities. Their articular 

 surfaces are compressed, and present an obtuse trochlear angle but no 

 keel; they reach to the base of the condyle of tbe median metatarsal 

 behind. The latter is very convex above, slightly flattened below. The 

 lateral digits only reach to the distal end of the first phalange. The 

 penultimate phalange of each is much produced behind; the last or 

 ungueal, is much compressed, and is literally a half-hoof. The coronet 

 is half as long as the pastern, and the unguis or coffin-bone is acumin- 

 ate in outline and elevated on the middle line. It is deeply fissured at 

 the extremity, and the margin abounds in foramina. Tlie nutritious, 

 foramina of the base are each in the apex of a triangular fossa which i» 

 open posteriorly. This bone has proportions not unlike those ascribed 

 by Leidy to a specimen from the Niobrara, but is rather smaller ; but 

 the foot to which it pertains measures but 10.5 inches, while that of 

 P. sejunctus (without tarsals) is eleven inches in length. 



2Ieasurements. 



Length of atlas (extreme) 0.061 



Width of atlas, medially below q35 



Width of atlas in front of diapophyses OGO 



Length of odontoid process 023 



Length of three posterior dorsal vertebrte Q7g 



Diameter of articular face of centrum, (transverse) 021 



Diameter of articular face of centrum, (vertical) 015 



Length of humerus (axial) 192 



Diameter proximal end, (anteroposterior) 0(5 



Diameter proximal end, (transverse) 0c5 



2gb 



